We propose to study the genetics of human and rodent cells in culture using the techniques of somatic cell genetics. Our goal is to increase our understanding of human genetics, including gene amplification, gene mapping, and the pathogenesis of inherited diseases of purine metabolism. We will study the mechanism of gene amplification in human-mouse somatic cell hybrids. The genes to be studied include dihydrofolate reductase, aspartate transcarbamylase, ribonucleotide reductase, and adenosine deaminase. The hybrid clones that contain these amplified genes will be selected in media containing, respectively, aminopterin, phosphonoacetyl-L-aspartate, hydroxyurea, and arabinosyladenine. We will analyze their karyotypes with the expectation that the amplified genes will be localized on separate, specific human chromosomes. The clones, each of which retains multiple copies of a specific human chromosome, will be used for human gene mapping studies. We will derive variants from a mouse macrophage-like cell line J774. The mutant phenotypes include deficiencies in one or several of purine salvage enzymes. These lines will be studied biochemically in order to delineate the molecular pathology of immunodeficiency diseases associated with purine enzyme deficiencies. We will also isolate variants lacking functions in the pathways of tubercidin (an adenosine analogue) incorporation. These lines will be used for intraspecific hybridization experiments, complementation tests as well as biochemical characterization of the heritable defects. In addition, they will be hybridized with human cells for the purpose of analyzing corresponding human cellular functions.